1. Field of the Invention
The present invention relates to an optoelectric integrated device in which light-emitting and light-receiving devices are arranged on the surface of a three-dimensional solid semiconductor crystal, such as a ball-shaped silicon (Si) substrate (referred to as a Si ball in this specification). The optoelectric integrated device is typically an optoelectric processing unit which is applicable to a neurocomputer and the like.
2. Related Background Art
One conventional method of rapidly operating a central processing unit (CPU) is to narrow the width of the electric wires used therein and to increase the integration density. This method is, however, accompanied with the pin-bottle-neck problem that the integration density is restricted by the number of electric wires, which drastically increases as the number of devices increases. Several methods for solving this problem have been proposed as follows.
(1) Optical wiring
This method aims to solve the pin-bottle-neck problem by replacing a portion of the electric wiring by optical wiring. The total number of electric wires can be reduced owing to characteristics of non-electromagnetic induction and broad band of the optical wiring. However, when the optical wiring is arranged using conventional optical fiber and semiconductor waveguides, the width of the optical path becomes far thicker than that of electric wires. Accordingly, only a limited portion of the electric wiring can be replaced by optical wiring, and the resultant configuration inevitably lacks flexibility.
The method of an open system (e.g., spatial transmission) has also been proposed. In this case, high density wiring is possible since the degree of freedom of the spatial transmission line itself is large. However, the positional alignment between light-emitting and light-receiving devices is exceedingly complicated, and high density integration is hard to achieve. Thus, the total processing capability becomes smaller than the case where only electric wiring is used.
(2) Si ball with integrated circuit (IC) thereon (ball IC)
The use of a Si ball has been proposed as one solution of the above problem, by a structure that uses only electric wiring. The integration degree per unit volume increases in inverse proportion to the radius of the Si ball since the Si ball uses its spherical surface, whose spatial-use efficiency is larger than that of a conventional planar Si substrate. Further, the wiring length decreases, and accordingly the processing speed is expected to increase due to the effect of integration degree multiplied by the wiring length. This method is, however, not a decisive method from the view point of high speed operation. The reason therefor is that wire width and wire interval decrease as the ball radius decreases, and accordingly adverse influences of high resistance and electromagnetic induction noise rapidly increase.
As described in the foregoing, a method for radically solving the pin-bottle-neck problem and achieving a high speed processing unit has not yet been proposed at present.
It is an object of the present invention to provide an optoelectric integrated device, such as a processing unit applicable to ultra-high speed operation, ultra-parallel processing and the like, which can solve the above pin-bottle-neck problem, and in which optical devices are arranged on the surface of a three-dimensional solid semiconductor crystal and the interior of the semiconductor crystal is used as an optical transmission line.
The present invention is generally directed to an optoelectric integrated device which includes a three-dimensional solid semiconductor crystal, and a plurality of optical devices including a light-emitting device and a light-receiving device integrated on the surface of the semiconductor crystal, and in which light is emitted and received between the light-emitting device and the light-receiving device through the interior of the semiconductor crystal used as an optical wiring medium. The present invention is also generally directed to an optoelectric integrated device which includes a spherical semiconductor, and at least one of a light-emitting device for emitting signal light into the interior of the spherical semiconductor and a light-receiving device for receiving signal light transmitted through the interior of the spherical semiconductor.
In those structures, the solid semiconductor crystal is typically a silicon (Si) crystal on which electronic devices, such as a field effect transistor (FET) and a transistor, can be easily formed monolithically. If adaptable, other semiconductor crystal, such as germanium (Ge), can also be used. The three-dimensional configuration is typically a sphere or ball, but other configurations, such as a cubic one, can also be used. An important feature of the present invention is to construct an optoelectric integrated device in which the interior of a solid semiconductor crystal, such as a Si ball, is used as an optical transmission line and that an optical device (typically, optical devices and IC) is integrated on the surface of the semiconductor crystal.
The optical device can include a portion composed of III-VN semiconductor material, such as GaNAs, GaInNAs, AlNAs, and GaInNAsP, or IV semiconductor material, such as SiGe. In this specification, xe2x80x9cIII-VN semiconductor materialxe2x80x9d indicates III-V compound semiconductor material that contains nitrogen (N) as a V material.
On the basis of the above structure, the following more specific structures are possible.
The optical device can be formed on a buffer layer for lattice matching which is formed on the surface of the semiconductor crystal. The buffer layer adjusts or compensates for a difference in lattice constant between the semiconductor crystal and the optical device to secure a crystal growth having a good performance.
The light-emitting device can be constructed such that it emits spontaneous emission light or induced emission light into the interior of the semiconductor crystal. The wavelength of the light is longer than a bandgap wavelength of the semiconductor crystal such that the light cannot be absorbed by the semiconductor crystal.
The light-emitting device can be constructed such that it emits light into the interior of the semiconductor crystal, and one or a plurality of the light-receiving devices can be arranged such that those receive the light emitted by the light-emitting device. The light-emitting device may also be constructed such that it emits spontaneous-emission light or induced-emission light into the exterior of the semiconductor crystal.
The light-receiving device can be arranged such that it receives light emitted into the interior of the semiconductor crystal by one or a plurality of the light-emitting devices. The light-receiving device may also be arranged such that it receives light from the exterior of the semiconductor crystal.
The light-emitting devices can include a light-emitting device which can emit light into the interior of the semiconductor crystal toward a predetermined light-receiving device, and a light-emitting device which can emit light into the interior of the semiconductor crystal toward a plurality of predetermined light-receiving devices. Thereby, flexible wiring can be constructed with high integration.
The optical devices and an electronic device can be integrated on the surface of the semiconductor crystal, and the electronic device has at least one function of switching on and off the light-emitting device, converting light received by the light-receiving device into an electric signal, and performing arithmetic and logical operations on the basis of the electric signal.
As described above, therefore, the interior of a solid semiconductor crystal is used as an optical path for optical interconnect.
In a typical structure, the wiring for electric connection is formed on the surface of a Si ball with one or more IC""s thereon (a ball IC), and the interior of the ball IC is used as an optical interconnect path. In such a structure, a light-emitting device formed on the Si ball needs to have a wavelength band which cannot be absorbed by Si. Further, optical devices need to operate in the same environment as Si.
In the preferred embodiments of the present invention, the above requirements are typically satisfied by a structure in which the light-emitting device is composed of III-VN semiconductor material, and the light-receiving device is composed of III-VN semiconductor material or SiGe. The III-VN semiconductor material represented by GaNxAs1xe2x88x92x lattice-matches to Si when x is approximately equal to 0.2. When x is approximately equal to 0.03, an active layer composed thereof can emit light at a wavelength of about 1.3 xcexcm which cannot be absorbed by Si. Further, highly-efficient light emitting diodes (LED) and surface emitting lasers (such as a vertical cavity surface emitting laser (VCSEL)) can be constructed since a multi-layer film of GaNAs/AlNAs can be used as a highly-reflective mirror.
The light-receiving device can also be fabricated by substantially the same construction. Further, the light-receiving device can be more easily fabricated by using Si/Ge. The light-emitting device, such as LEDs, formed on the semiconductor crystal can radiate light into the interior thereof, and have all the light-receiving devices, such as photodiodes (PDs), receive the emitted light. Thus, the interior of the semiconductor crystal can be used as a three-dimensional optical transmission path. When a laser diode (LD) with a sharp directivity factor is used as a light source, light emitted thereby can be transferred to a predetermined light-receiving device.
The light source and the light-receiving device can be controlled by the electronic circuit arranged nearby. The electronic circuit arranged near the light-receiving device can not only convert light into an electric signal but also include an arithmetic and logic circuit capable of performing a desired processing therein. A signal received by the light-receiving device can be processed by ICs in its neighborhood. The processed result can be transmitted through the electric wiring formed on the surface of the semiconductor crystal, or newly transmitted toward the interior of the semiconductor crystal as an optical signal. A final processed result can be supplied to the exterior of the semiconductor crystal as an electric signal or optical signal.